These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Cytochrome c oxidase: biphasic kinetics result from incomplete reduction of cytochrome a by cytochrome c bound to the high-affinity site.
    Author: Ortega-Lopez J, Robinson NC.
    Journal: Biochemistry; 1995 Aug 08; 34(31):10000-8. PubMed ID: 7632672.
    Abstract:
    The electron-transfer kinetics of cytochrome c oxidase were probed by measuring the reduction levels of bound cytochrome c, cytochrome a, and cytochrome a3 during steady-state turnover. Our experimental approach was to measure these reduction levels as a function of (1) the rate of electron input into tightly bound cytochrome c by varying the concentration of TMPD (N,N,N',N'-tetramethyl-p-phenylenediamine) and/or cytochrome c and (2) the rate of electron efflux out of cytochrome a (true Kcat) by changing the detergent surrounding cytochrome c oxidase. In most detergent environments, the rate of electron input into cytochrome c is not faster than the rate of electron efflux from cytochrome a. The relatively slow rate of electron input results in incomplete reduction of both cytochrome a and cytochrome c bound a the high-affinity site unless Kcat is very slow. When the high-affinity site is saturated with cytochrome c, the steady-state reduction level of cytochrome a defines Vmax,1, which is the maximum velocity of the high-affinity phase. The remaining fractional oxidation level of cytochrome a determines Vmax,2, the maximum velocity of the low-affinity phase. Therefore, it is the sum Vmax,1 + Vmax,2 which defines the maximum rate of electron transfer between cytochrome a and the bimetallic center, i.e., Kcat. We also were able to evaluate the true Kcat of cytochrome c oxidase in each detergent environment directly from the steady-state reduction levels without any of the complications introduced by the analysis of the polarographic kinetic data.(ABSTRACT TRUNCATED AT 250 WORDS)
    [Abstract] [Full Text] [Related] [New Search]